Preheat your oven to 400°F (200°C) and grease a ceramic baking dish with butter.

Peel and thinly slice the Yukon gold potatoes, about 1/8 inch thick.

Melt 4 tablespoons of unsalted butter in a large pot over medium heat and sauté minced garlic for 1 minute until fragrant.

Sprinkle in 1/4 cup of all-purpose flour, stirring to create a roux, and cook for 1-2 minutes.

Gradually whisk in 2 cups of heavy cream and stir until the mixture thickens, about 5 minutes.

Stir in 1 cup of grated Parmesan cheese, 1 teaspoon of fresh thyme, kosher salt, and black pepper until combined.

Fold the sliced potatoes into the creamy mixture until evenly coated.

Arrange the coated potato slices upright in a greased baking dish and pour any remaining sauce over the top. Sprinkle with 1/2 cup of Parmesan.

Cover with aluminum foil and bake for 30 minutes, then remove foil and bake for another 30 minutes.

Let the dish rest for 10 minutes before serving.